Generally, an electronic photocopying process or an electrostatic printing process includes the steps of: (1) forming an electrostatically-charged image or an electroconductive image (hereinafter, referred to as “electrostatic latent image”) on the surface of an electrostatic recording material drum, for example, an organic photoconductor (OPC) drum; (2) electrostatically attaching a charged toner to the drum to develop and visualize the electrostatic latent image formed on the surface of the drum; (3) transferring the developed toner image to a recording medium such as paper, a recording film or the like; and (4) fixing the image transferred to the recording medium using a thermal press roller or the like.
Such an image-forming process is widely used in the fields of copiers and printers because printed material can be obtained rapidly, the control stability of the image formed on the surface of electrostatic recording material drum is excellent, and an image-forming apparatus can be easily handled.
In the step of developing the electrostatic latent image, the toners used in dry development are classified into one-component toners, two-component toners, and the like. The two-component toner includes a magnetic body for developing and transferring the electrostatic latent image formed on the drum together with a binder resin, a colorant, a charge adjuster, and other additives, and is prepared in the form of particles by melting, kneading, dispersing, finely pulverizing and classifying these toner components. The binder resin, which is the main component of the toner, must have excellent colorant dispersibility, attachability, non-offset ability, storage stability, and other electrical properties as well as excellent transparency, and must form a clear image even when a small amount of a colorant is used. Further, preferably, the binder resin must have a wide color tone range, be able to improve the image quality of copies or prints, and must be environmentally friendly.
Conventionally, a polystyrene resin, a styrene acrylate resin, an epoxy resin, a polyamide resin or the like have been used as the binder resin. Recently, polyester resins having excellent attachability and transparency have been increasingly used. However, currently, raw materials of many products including the toner are being prepared from fossil resources such as petroleum and the like. Therefore, in order to prevent the depletion of the fossil resources, it is very important to reduce the use of fossil resources. In particular, a raw material of most of the toner resin, which is 70% or more of the toner, is petroleum, thereby causing the problem of petroleum resources becoming depleted and the problem of global warming attributable to the large consumption of petroleum resources and the discharge of carbon dioxide into the atmosphere. When a plant-derived resin growing using carbon dioxide in the atmosphere is used as the toner resin, it is possible to solve both the problem of global warming and the problem of the depletion of petroleum resources because carbon dioxide is recycled by the system itself. Particularly, biomass obtained from plant-derived polymers is receiving considerable attention.
Biomass is referred to as “biological organisms” including microbes, plants performing photosynthesis using solar energy, fungi, and animals. Further, biomass resources include: starch-based resources including cereals and potatoes; cellulose-based resources including agrofishery products such as herbs, rice straws, chaffs, etc.; environmental circulation resources derived glucidic plants such as sugarcane, sugar beet, etc.; and protein-based resources including excretions of cattle, corpses of cattle, microorganisms, and fungi. Biomass resources also include organic waste, such as paper, residue of food, etc.
Such biomass can be practically used as a biological resource, which can become an energy source or various synthetic raw materials, by combining biological technologies with chemical technologies. The best advantage of biomass is that it can be reproduced. That is, differently from other fossil fuels, biomass does not become depleted, and is environment-friendly because carbon dioxide discharged to the atmosphere by combustion is obtained from the atmosphere for several years by the growth of animals, plants and microbes and thus the amount of carbon dioxide in the atmosphere does not increase. Therefore, biomass can replace conventional petrochemical products.
In order to solve the above-mentioned problem, several technologies that use biomass as the raw material of a toner resin have been proposed. For example, Japanese Unexamined Patent Publication Nos. 2009-75544, 2008-250171, 2001-166537, 1997-274335, 1994-308765 and 1994-200250 disclose technologies of using a polylactic acid resin as a toner resin. However, these technologies are problematic in that, when a polylactic acid resin is directly or partially used, it is difficult for the polylactic acid resin to serve as a thermoplastic resin in an attaching process because the ester bond concentration of the polylactic acid resin is higher than that of general polyester resin. Further, these technologies are problematic in that the toner made in this way becomes very hard, so that the toner cannot be sufficiently grinded, and its production rate is low. Furthermore, these technologies are problematic in that a large amount of fine powder is produced by the mechanical shock attributable to being agitated in a developer, thus causing offset and aggravating image degradation.
Meanwhile, the molecular weight of polylactic acid cannot be easily controlled because it uses only carbon atoms and has an ester bond, so that it is difficult to obtain the physical properties required of a toner that uses only polylactic acid. Further, polylactic acid cannot sufficiently keep up with an image forming apparatus at the time of forming a black image, thus causing fusing defects. Furthermore, polylactic acid is problematic in that its long-term storage stability gets worse in order to provide good biodegradability to toner. That is, when a toner made of polylactic acid is left for a long period of time under the conditions of high temperature and high humidity, the toner is hydrolyzed, and thus the toner cannot be used. Further, when prints are left for a long period of time while overlapping with each other, the prints may become attached to each other because of softened toner.
In order to solve the above problems, conventionally, methods of providing the physical properties and thermal characteristics required of a toner by mixing polylactic acid with other resins have been used. However, since the compatibility and dispersibility of o polylactic acid to a polyester resin and a styrene-acrylate copolymer generally used in the toner are very poor, it is very difficult to prepare a toner using a mixture of polylactic acid and other resins. Further, International Patent Application No. PCT/US2006/010136 discloses a toner resin using isosorbide and dimer acid which are plant-derived environmental circulation polymerization raw materials. However, since this toner resin is expensive, it is difficult for this toner to be commercially used, and it is difficult to increase the amount of biomass in the toner.
Generally, a polyester resin, which is used as a binder resin in toner, includes bisphenol-A or a derivative thereof as an alcohol component. However, since bisphenol-A is a compound harmful to the environment, there have been attempts to develop a polyester resin which does not include bisphenol-A or a derivative thereof, which has excellent offset resistance, low-temperature attachability, sharp melt properties, blocking resistance, electrostatic characteristics, grindability, storage stability, transparency and the like and which can form a good developed image even after being left for a long period of time.
Germanium-based catalysts, antimony-based catalysts, tin-based catalysts and the like have been used to manufacture a polyester resin for toner. However, these catalysts are problematic in that they are not environmentally preferable because they are used in an excess amount due to low activity, and in that they deteriorate the transparency of a polyester resin because they have their own coloration characteristics (for example, antimony-based catalysts exhibit gray coloration). Therefore, attempts are being made to improve the reactivity and transparency of a polyester resin using titanium-based catalysts such as tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, polybutyl titanate, ethylacetoacetic ester titanate, isostearyl titanate, titanium dioxide, a TiO2/SiO2 coprecipitant, a TiO2/ZrO2 coprecipitant, and the like.